Most of the matrix protein that is deposited in enamel during the secretory stage is lost during the postsecretory development of enamel. This protein loss is preceded by marked decreases in the molecular weights of the matrix proteins. It has been postulated that this molecular weight decrease is accomplished by a proteolytic enzyme that is secreted with the matrix. A serine protease activity in developing enamel has been reported. In preliminary studies, we have isolated a proteolytic enzyme from embryonic bovine secretory enamel. This enzyme represents a small fraction of the total matrix protein, and it has very low activity until it is separated from the bulk of the protein by affinity chromatography. The enzyme calcium-activated. This project is designed to further characterize this enzyme and to study its effect on developing enamel matrix. The specific aims are as follows: (1) to purify the serine protease and to determine the specificity of bonds cleaved by this enzyme using model substrates and enamel matrix; (2) to determine whether the enzyme hydrolyzes amelogenins, enamelins, or both; (3) to determine whether the enzyme is secreted as a protenzyme or with an inhibitor; and (4) to determine whether inhibitors of the enzyme inhibit the in vitro loss from enamel of previously synthesized matrix proteins.